Sizing polyester yarns with an ethylene-maleic interpolymer



United States Patent SIZING POLYESTER YARNS WITH AN ETHYL- ENE-MALEIC INTERPOLYMER John H. Johnson and Joseph E. Fields, Dayton, Ohio, assignors to Monsanto Chemical Company, St. Louis, Mo., a corporation. of Delaware No Drawing. Application December 30, 1955 Serial No. 556,394

18 Claims. (Cl. 117-1383) This invention relates to sized polyester yarns. In some of its aspects, the invention pertains to an improved SIZ- ing material for use on warp yarns made of high molecular weight fiber-forming polyesters, such as polyethylene terephthalate. In other aspects the invention perta ns to improved methods for sizing polyester yarns.

The advent of polyester yarns has presented many problems to textile manufacturers in finding a composition which can be used as an efiicient sizing material. Due to the chemical and physical properties ofpolyester yarns, the usual materials used as sizes for natural yarns such as cotton and wool yarns and synthetic yarns of the type of viscose and acetate yarns are not effective on polyesters. Further, although fiber-forming polyesters and nylon (fiber-forming linear super--polyamides) are somewhat related in some of their properties, their chemical natures are quite different, and a material effective to size nylon yarns is not necessarily effective to size polyester yarns, and similarly a material effective to size polyester yarns is not necessarily effective to size nylon yarns.

An important drawback of certain materials that have been, tried for sizing polyester yarns is that supplementary additives are essential to obtain results sufficiently satisfactory to permit practical use. Such supplementary materials include lubricants, Wetting agents, urea, etc. These not only increase the cost of the sizing composition but often make the removal of same, afterthe weaving operation, much more difiicult. Thus, the scrubbing operation for removal of size takes longer and is more expen- 'sive when an oily lubricant has beenused. Another drawback of conventional polyester sizes. is that afterwaxing maybe required. This involves applying the size, drying the sized yarn, and then applying a wax to the sized yarns before they can be used. in knitting machines. Again, the cost is increased, and the scrubbing operation made more difiicult.

' Polyester yarn of high twist, such as 25 or more turns per inch, is used in weaving marquisette and no sizing is required. However, this represents a quite small proportion of the total polyester yarn usage at the present time. For weaves in which the warp yarn must have a lower twist, a size is necessary, but mill operators feel that all of those so far offered on the market have severe drawbacks.

In accordance with the present invention, polyester yarns, preferably but not necessarily warp yarns made of continuous filaments of polyester, are sized with a watersoluble free acid form of an ethylene/maleic interpolyn er having from zero to 10.0 percent of its maleic units mono-esterified with an aliphatic alcohol, the said interpolymer in said free acid form having a specific viscosity of at least 0.1 as determined on a one weight percent solution thereof in dimethylfonnamide at 25 C. These materials are absolutely non-tacky, even under severe humidity conditions. In contrast, the alkali metal salts, e.g., the, sodium salts, of some of these materials, particularly those of low molecularweight, tend towards tackiness, and the higher the humidity the more tacky they 0 ice become. The alkali metal salts are also found to be far inferior as polyester sizing agents, and in fact are of no practical interest whatsoever to those concerned with the sizing. and weaving of polyester yarns. It is essential 1n the practice of the invention that the ethylene/maleic interpolymers be employed in their non-tacky free acid form.

In preferred embodiments of the invention, polyester yarn is sized with ethylene/maleic anhydride copolymer which has been converted to. water-soluble free acid form. This is very readily accomplished simply by dissolving the ethylene/maleic anhydride interpolymer in warm water, e.g., by introducing the anhydride form of the interpolymer in the desired quantity into water heated to say -95 C. and vigorously agitating same, which will permit complete solution to occur within a period of approximately 10 minutes to one hour. The result is an aqueous solution of the interpolymer in water-soluble free acid form, most or all the anhydride groups under these conditions being hydrolyzed to form two carboxylic acid groups per maleic anhydride group originally present in the molecule. Some mill operators will prefer to receive the polymer in the anhydride form, paying lower freight costs, and put it into solution, as just described, at the mill. Others, however, will prefer that the ethylene/maleic anhydride interpolymer be hydrolyzed as a separate operation prior to its shipment to the place of use as a sizing agent. This is readily done by the solution procedure just described, followed by dryingthe aqueous solution, e.g., by spray drying or in a tray-type drying oven under a vacuum and at moderate temperatures of from say 50 to 90 C. A more desirable physical form of the solid water-soluble free acid polymer, however, is obtained. by subjecting the polymer in its anhydride form to the'action of water vapor. For example, the anhydride form of the copolymer can be subjected to a relative humidity of 70 to 90 percent, at a temperature of 5.0 to 90 C., for a period ranging from one-half hour tosay 5 to 10 hours sufficient to effect hydrolysis of an adequate. number of anhydride groups to carboxylic acid groups to give. the polymer the property of promptwater solubility. It is preferred to effect this vapor-phase hydrolyisis until substantially complete hydrolysis to the free acid form has occurred. In any event, the ethylene/maleic anhydride interpolymer is prepared by interpolymerizing ethylene with maleic anhydride under such conditions as to give a polymer in the anhydride form which, on hydrolysis to free acid form, exhibits a specific viscosity of at least about 0.1 as determined on a one weight percent solution thereof in dimethylformamide at 25 C. Generally speaking, such an interpolymer having a specific viscosity determined in the same way on the anhydride form, of about 0.05 to 0.07 will have in the free acid form the desired minimum specific viscosity of about 0.1. In general, the specific viscosity of the free acid form of an ethylene/maleic anhydride interpolymer will be somewhat less than twice the specific viscosity of the same polymer in the anhydride form. Ethylene/maleic anhydride interpolymers which have been hydrolyzed in any manner to the free acid form consist essentially of regularly recurring units of the formula In order to impart added desirable properties, particularly for certain special sizing applications, we can prepare an ethylene/maleic interpolymer having a portion, up to percent, of its maleic units mono-esterified with an aliphatic alcohol. This is preferably done by;- reacting an ethylene/maleic anhydride interpolymer with,

a lower fatty alcohol, e.g., methanol, ethanol, isopropanol, n-propanol, n-butanol, sec.-butanol, tert.-butanol, isobutanol, the various amyl alcohols, etc. While unsaturated alcohols and those carrying non-hydrocarbon substituents, e.g., chloro, nitro, or others that do not react with the maleic anhydride units, can be used, there is generally no advantage and they are more costly. Higher alcohols such as those containing from 8 to 10, 15, or even 20 or more carbon atoms per molecule, of any of the possible straight-chain or branched-chain configurations, and constituting primary, secondary, or tertiary alcohols, can also be used for special situations, but in general a lesser percentage of the maleic units should be esterified with such higher alcohols than in the case of the lower alcohols because of water solubility limitations. However, such limitationscan be minimized by employing as aliphatic alcohol esterifying agent a watersolubilizing alcohol, e.g., an ether-alcohol made by reacting several moles of ethylene oxide with a lower aliphatic alcohol. For example, a suitable oxa-alkanol, i.e., ether-alkanol, is made by condensation reaction of isopropanol with ethylene oxide, the resulting alcohol (actually a mixture of alcohols) having the structural formula CH -OH OH wherein the average value of n is from 2 to 10. Esterification is readily effected by mixing the ethylene/maleic anhydride interpolymer with the chosen alcohol or a mixture of alcohols, and refluxing the mixture until the desired degree of esterification is achieved. An alternative, but generally less desirable, preparation of an ethylene/maleic interpolymer having at least a portion of its maleic units mono-esterified with an aliphatic alcohol, involves interpolymerizing ethylene with a comonomeric material comprising a maleate monoester, e.g., monomethyl maleate, monoethyl maleate, mono-isopropyl maleate, mono-n-butyl maleate, monododecyl maleate, maleic acid mono-esterified with water-solubilizing oxa-alcohols such as those described above, and the like. These materials can also be described as monoesters of maleic acid, or as acid esters of maleic acid. The discussion above concerning relation of percentage of maleic units esterified, size and type of the alcohol, and water solubility, applies also when a maleate monoester is employed as a monomer. In the limiting case, the comonomeric material to be copolymeriz ed with ethylene consists entirely of maleate monoester. It is preferred that the comonomeric material also comprise maleic anhydride, so that the ethylene is interpolymerized with a mixture of maleic anhydride and one or more maleate monoesters. It is also to be understood that where the comonomeric' material consists of maleate monoester, such maleate monoester can be a single species or a mixture of maleate monoesters. In any event, whenever maleic anhydride units are present in the interpolymer, the interpolymer is subjected to hydrolysis under conditions converting same to free acid form. The polymers presently preferred in the practice of the invention are ethylene/maleic interpolyme'rs having from zero to 50 percent of the maleic units therein mono-esterified with an aliphatic alcohol, by which language is understood the esterification can be by virtue of esterifying maleic anhydride units in a pre-prepared interpolymer and/or by the use of a monoester of maleic acid as a comonomer in preparing the polymer. Regardless of the presence or absence of mono-esterified maleic units in the interpolymer to be used, the interpolymer in free acid form should be water-soluble, i.e., at least 1 part by weight can be dissolved in 100 parts by weight water at20 C., and should having a specific viscosity of at least about 0.1 determined as hereinabove mentioned. In most instances the polymer used will have a specific viscosity within the range of about 0.3 to 4, although those of even higher specific viscosity than 4 are within the broad scope of the invention. In general, the higher molecular weight polymers are more effective than the lower molecular weight; hence we prefer to employ those which have a specific viscosity of at least about 2. All of these specific viscosities referred to here are deter mined on the polymer in its free acid form, in a one weight percent solution of the polymer in dimethylformamide at 25 C.

The following examples illustrate some features and advantages of the invention. It will be understood of course that variations from the exact details shown can be made without departing from the invention.

Example 1 A. A 3-liter rocking autoclave was charged with 1600 ml. benzene, 200 grams maleic anhydride and 2.56 grams benzoyl peroxide. It was charged with ethylene to give a pressure of 600 pounds per square inch gauge, and Was maintained at this pressure during the reaction. The reaction temperature was maintained at 70 C.

When polymerization had ceased, as evidenced by no further tendency of the pressure to drop, excess ethylene was bled otf and the reactor opened. The ethylene/maleic anhydride interpolymer, present as a slurry of fine particles in benzene, was separated by filtration and dried in a vacuum oven at C. for about 20 hours. The yield of interpolymer was 255 grams, which was 99% of theory, based on maleic anhydride charged.

The specific viscosity of this ethylene/maleic anhydride interpolymer, as determined on a one weight percent solution thereof in dimethylformamide at 25 C., was 1.26.-

B. In the same apparatus and by the same procedure as described in A, the autoclave was charged with 1600 ml. of benzene, 200 grams maleic anhydride and 2.56 grams of benzoyl peroxide (0.26 mole percent based on theoretical reacting monomers). Polymerization temperature was 60 C. Ethylene was charged to give a pressure of 400 pounds per square inch gauge, and this pressure was maintained throughout the polymerization by additional charging of ethylene when required.

The ethylene/maleic anhydride interpolymer was recovered as in A, in a yield of 252 grams, which was 98% of theory based on maleic anhydride charged.

The specific viscosity of the interpolymer, determined in the same way, was 1.293.

C. A blend of the ethylene/maleic anhydride interpolymers of A and B above was prepared in a total weight of 400 grams. The specific viscosity of the blended polymer, as obtained by averaging the specific viscosities of the two polymer preparations of A and B, was about 1.28.

This blend was exposed in trays in a closed oven to a temperature of 70 C. and an air atmosphere of 70% relative humidity. After a little over 7 hours time, substantially complete hydrolysis of the maleic anhydride units in the interpolymer had occurred, and the resulting free acid form of the interpolymer was completely watersoluble.

The specific viscosity of the hydrolyzed free acid form of the ethylene/maleic interpolymer whose preparation has just been described, was determined on a one weight percent solution thereof in dimethylformamide at 25 C. The specific viscosity of the free acid form determined under these conditions was 2.22.

Example 2 A. In the manner of Example 1, ethylene and maleic anhydride were interpolymerized in three separate batches, using benzene as diluent, 'lauroyl peroxide as catalyst, ethylene pressure maintained at 600 pounds per square inch gauge and a reaction temperature of 50 C. The three batches were then mixed together in the slurry 5 form. before filtering. The filtered polymer was washed several times with benzene, and dried in a 100 centigrade oven for 24 hours under vacuum. The specific viscosity of this ethylene/maleic anhydride copolymer, determined on a one weight percent solution thereof in dimethylformamide at 25 C., was 1.57.

B. As described in paragraph C of Example 1, the interpolyrner whose preparation is described in paragraph A of this Example 2, was subjected to hydrolysis by being maintained at conditions of 70 C. and 70% relative humidity until complete conversion to the free acid form resulted. This material was freely soluble in water. The specific viscosity of the thus-hydrolyzed water-soluble free acid form as determined on a one weight percent solution thereof in dimethylformarnide at 25 C., was 2.71.

Example 3 The effectiveness of the products of Examples 1 and 2 as size for polyester yarns was. determined. To conduct the, test, a 5 to 6 weight percent aqueous solution of each of the polymers was prepared. Polyethylene terphthalate (sold under the trade-name Dacron) warp yarns were drawn through the solution at a rate of about 10 to 20 yards a minute and then passed through squeeze rolls adjusted to exert a pressure of about 10 to 20 pounds per linear inch. The yarns were then dried by passing them over a series of five heated metal drying cans.

Yarns thus treated have a sizing of the interpolyrner firmly adherent thereto. The sizings are tough and abrasion resistant. The sized yarns may be Woven easily and efliciently using standard weaving techniques. Additives, such as urea, surfactants, etc., need not be used.

The abrasion resistance of the polyethylene terephthalate yarns sized with the interpolymers of Examples 1 and 2 were tested in a standard abrasion testing apparatus with the results being reported in arbitrary units ranging from 20 to 1, with 20 being nearly perfect resistance to abrasion and 1 being substantially no abrasion resistance as measured by this test. The following results were obtained:

Abrasion Resistance Cycles 20 Material:

Unsized Sized with Example 1 product. Sized with Example 2 product.

and 20 cycles showed little loss in abrasion resistance.

Even at 20 cycles the yarns had substantial abrasion resistance.

The interpolymers employed in the present mvention are readily prepared by a variety of polymerization procedures. Preferably, ethylene is interpolymerized with maleic anhydride, or with maleic anhydride plus one or more maleate monoesters, or with one or more maleate monQQSters in the absence of maleic anhydride, in the presence of a liquid organic diluent and a free radical liberating catalyst.

, The following preferred reaction conditions refer partic larly t0 the copolymerization of ethylene with maleic anhydride. When substituting maleate monoester for part or all ,of the maleic anhydride, the same general procfidlll'cs are used but somewhat more stringent conditions,

.i,e., higher temperature, higher pressure, and/or higher catalyst concentration, may be required since the maleate 6 monoesters enter into the interpolymerization reaction somewhat less easily than does maleic anhydride.

We prefer to employ a reaction temperature within the range of 40-90 C. and 45 to C. is especially advantageous. At such temperatures, the reaction rate is good and the physical form of the interpolymer product is good. However, temperatures outside these ranges can be used.

The reaction pressure can be atmospheric or below, but is preferably superatmospheric. It is preferred that the reaction be carried out in a closed vessel such as a stirred autoclave, rocking bomb, tubular reactor through which reaction mixture flows, or the like, at a pressure above atmospheric pressure. The pressure is preferably above pounds per square inch gauge, and pressures of 200 and 600 pounds per square inch gauge are especially preferred. However, even higher pressures, say up to 1000 pounds per square inch, or even higher such as up to 5000 pounds per square inch and above, are permissible. In general, the higher the temperature the lower the molecular weight, and the higher the pressure the higher the molecular weight.

The copolymer product of ethylene and maleic anhydride contains essentially one mole of ethylene per one mole of maleic anhydride combined therein, irrespective of the relative proportions of ethylene and maleic anhydr-ide introduced into the reaction system. The ratio of free ethylene available for reaction at any given time depends upon a variety of factors, including particularly the quantity of free maleic anhydride dissolved in the solvent and the quantity of ethylene dissolved in the solvent. The latter value in turn depends upon the solubility of ethylene in the reaction mixture, which is a function of the particular solvent, the temperature, the pressure, and the concentration of maleic anhydride in the solvent. it is much preferred that by the time the reaction has been completed, an excess of ethylene over that required to react with the entire quantity of maleic anhydride shall have been furnished to the reaction mixture, so as to give maximum utilization of the maleic anhydride. Any unreacted ethylene is readily recovered and recycled to the reaction. The ethylene, maleic anhydride, and solvent or diluent, can be brought together in various ways, but in any event thorough intermixture of same should be provided. Thus, the reaction can be conducted in a batch, into which ethylene is continuously or intermittently added to maintain pressure until all the maleic anhydride is used up by copolymcrization. A similar operation can be conducted wherein maleic anhydride is added continuously or intermittently. The components of the reaction mixture can be continuously fed into a stirred autoclave with continuous overflow of total reaction mixture out of the autoclave either through recovery steps or through a series of autoclaves. The total reaction mixture can be passed through an elongated reaction tube, with ethylene and/or maleic anhydride and/or catalyst being added at one or more points along the length of the tube if desired.

It is most convenient to carry out the polymerization reaction in the presence of a liquid organic diluent, especially one that is a solvent for the maleic anhydride. Such diluent is preferably a non-solvent for the copolymer product. Suitable diluents include aliphatic or aromatic hydrocarbons or chlorinated hydrocarbons, for example benzene, toluene, xylene, nhexane, mixed hexanes, octane, ethylene dichloride and the like, as well 'as mixtures of same. While the proportion of the diluent to the other components of the reaction mixture can be varied over a wide range, it is preferred to employ an amount such that the final reaction mixture will have a solids content (copolymer plus any unreacted maleic anhydride) within the approximate range of S to 60 weight percent.

The copolymerization is effected in the presence of a catalyst of free radical-promoting type, principal among which are peroxide-type polymerization catalysts and azo-type polymerization catalysts. Those skilled in the 'art are now fully familiar with a large number of peroxide-type polymerization catalysts and a suitable one can readily be chosen by simple trial. By way of example there can be mentioned benzoyl peroxide, lauroyl peroxide, 2,4-dichlorbenzoyl peroxide, tertiary butyl peroxide, tertiary butyl hydroperoxide, diacetyl peroxide, diethyl 'peroxycarbonate, dimethylphenylhydroperoxymethane (i.e., cumene hydroperoxide), hydrogen peroxide, potassium persulfate and the like. The azo-type polymerization catalysts are also well known to those skilled in the art. These are characterized by the presence in the molecule of the group --N=N- wherein the indicated valences can be attached to a wide variety of organic radicals, at least one however preferably being attached to a tertiary carbon atom. By way of example there can be mentioned a,a-azodiisobutyronitrile, azo methane, diazoaminobenzene, and the like. The peroxytype or azo-type or other free radical-promoting type of polymerization catalyst is used in small but catalytic amounts, which generally are not in excess of one to two mole percent based on moles theoretical reacting monomers charged, i.e., based on the sum of the moles maleic monomer charged plus the same number of moles of ethylene when the latter is present in at least the stoichiometric amount. A suitable quantity is often in the range of 0.1 to 1.0 mole percent.

The foregoing discussion of diluents, catalysts, reaction systems, etc., is also applicable to inteipolymerization of ethylene with comonomeric materials comprising maleate monoesters.

The interpolymer, however made, is advantageously separated from the bulk of the solvent by filtration or centrifuging, and then subjected to mild heating, preferably at sub-atmospheric pressures, for example at temperatures of 50 to 100 C., to remove residual solvent. It is often advantageous to precede this drying step by a washing step in which any unreacted maleic monomer is Washed from the polymer by use of a solvent such as benzene.

In the event maleic units in the ethylene/maleic interpolymer are to be mono-esterified by after-reaction of an interpolymer containing maleic anhydride units with an aliphatic alcohol, this esterification reaction can be eflected, for example, by adding to the slurry of polymer in solvent the calculated quantity of alcohol required for the degree of esterification desired and heating until esterification is substantially complete, e.g., 4 to 5 hours As pointed out hereinabove, any interpolymer containing maleic anhydride units is subjected to hydrolysis to convert the maleic anhydride units to free acid form, prior to use of the polymer as a size for polyesters. It is preferred to effect the hydrolysis as a preliminary step, preferably by contacting the interpolymer with water vapor under conditions resulting in hydrolysis of essentially all the anhydride groups to dicarboxylic acid groups. Or the hydrolysis can be effected by contacting a slurry of the interpolymer in an organic solvent with water,

or merely by mixing the interpolymer with water until it undergoes hydrolysis and dissolves in the water. The

resulting solution can be used directly as the size, or can can be esterified and still have an interpolymer which is water-soluble in the free acid form. This will not necessarily hold true, however, if instead of an alkanol, a water-solubilizing alcohol such as an ether-alcohol is employed. Some of the benefits of the invention can be retained even though an alkali, such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide be employed as an aid in solubilizing the interpolymer (which may sometimes be desirable when part or all the maleic units are esterified), so long as such quantity is very small in amount, say not over 0.2 mole sodium hydroxide per mole of maleic units in the interpolymer and in any event less than the stoichiometric amount that would be required to neutralize all the free carboxylic acid groups in the polymer. The interpolymer under such conditions is still considered to be in the free acid form. However, the use of much more alkali results in the presence of too high a proportion of the sodium or other salt in the sizing material. The sizing efficiency drops oif rapidly as the percentage of sodium salt increases and very much of the salt completely spoils the sizing effect. Accord ingly, it is much preferred to add no alkali or other saltforming cation whatsoever. Naturally, the industrial waters used in making up the size will generally contain a limited amount of cations (and associated inorganic anions and/ or hydroXyl ions), and the use of such waters is not outside the scope of the invention. However, the more ion-free the water used in dissolving the interpolymer to make up the size solution, the more satisfactory the results. It may be mentioned here that ethylene/ maleic anhydride copolymer converted to the free acid form dissolves in water to give an aqueous solution having a pH of about 2.2 to 2.5.

' and in a concentration sufficient to deposit a sizing quantity of the interpolymer on the .yarn, preferably between about 0.5 and 10 percent by weight of the interpolymer based on the dry weight of the polyester yarn. This may be accomplished in various ways, for example by passing the yarns through the size solution and beneath the surface thereof or by spraying the yarns with the size solu tion, and thereafter passing the yarns between squeeze rolls to remove excess solution and to deposit the required amount of the interpolymer. The size solution may also be applied in other ways, for example by dipping the yarns into a solution of the interpolymer. If squeeze rolls are used, the amount of pressure exerted upon the squeeze roll should be adjusted to remove sufiicient excess solution to deposit the required sizing amount of interpolymer on the yarn.

The size solution may contain, in addition to the inter polymer, small amounts, say 0.01 to 5 weight percent, of sizing adjuncts such as humectants, oils, wetting agents, and the like. As examples of humectants may be mentioned glycerine, ethylene glycol, sorbitol, propylene gly col, polyethylene glycols, polyglycerols, polypropylene oxides, and the like. Oils which may be used include the sulfonated animal, mineral and vegetable oils or mixtures thereof, water-emulsifiable mixtures of such oils with animal oils, mineral oils, vegetable oils, Twitchell oil, and the like. As examples of wetting agents may be mentioned acid-stable anionic wetting agents such as alkyl substituted benzene sodium sulfonates, in which the alkyl group contains from about 10 to 20 carbon atoms, alkali metal or ammonium monoalkyl sulfosuccinates, in which the alkyl group contains from about 10 to 20 carbon assavae atoms, and the like; and acid-stable non-ionic wetting agents such as the surface active condensation products of ethylene oxide with an alkylated phenol having from -8 to 20 carbon atoms in the alkyl group or an alkyl mer- 'it is preferred to dry the treated yarns at elevated temperatures of about 140 to 250 F. This may be accomplished by passing the treated yarns through an oven in which the circulating air is at a temperature of 140 to 250 F. or the treated yarns may be passed over one or more drying cans, which are heated at a temperature of 140 to 250 F., until the yarns are dry or contain less than 10% moisture.

The sized yarns are now ready for the Weaving operation and may be woven in a loom at a relative humidity between about 40 and 80%. Any suitable yarn, such as nylon, cotton, acetate, viscose, wool, polyester yarns and the like, may be used as the filling in the weaving operation. The size adheres to the polyester yarns during the weaving operation with only a limited amount of splitting or dusting off and protects the yarns from the mechanically moving parts of a loom. The interpolymer sizes disclosed herein are also sufficiently hard so that they dry on drying cans without sticking to the cans.

The size is readily removed from the warp yarns in the woven fabric by simple scouring with water, or soaping in a mild aqueous soap solution. This means that the fabric can then be treated with any suitable finishing agent to produce the desired finish on the fabric.

The term polyester as used herein is intended to include water-insoluble fiber-forming linear super-polyesters, particularly the water-insoluble fiber-forming linear polyesters prepared by condensing an aliphatic diol, such as ethylene glycol, with an aromatic polybasic acid, such as terephthalic acid. Such polyesters can also be prepared by other related reactions to provide the same moieties in the polymer molecule, for example by ester interchange of the diol with a diester of the acid, or by condensation of the dibasic acid with an ester of the diol, and the like. Fiber-forming polyesters can also be prepared by self-condensation of w-hydroxy carboxylic acids. Of the fiber-forming polyesters, it is preferred to size polyethylene terephthalate warp yarns, made of continuous filaments of polyethylene terephthalate, since they are commercially available, are especially amenable to sizing by the methods of this invention, and have excellent physical properties including high melting point, good strength and the like. Polyethylene terephthalate fibers are sold under the trademarks Terylene and Dacron, and are prepared commercially by ester interchange between dimethyl terephthalate and ethylene glycol.

The present invention is generically applicable to the sizing of fibers of any polyester. Many polyesters are fiber-forming, and thus of theoretical interest and can be sized in accordance with the invention, but as a practical matter may have such low melting points or other physical properties as not to be of commercial interest. By way of example of fiber-forming polyesters having comparatively low melting points, there may be mentioned especially the aliphatic polyesters, such as polytrimethylene hexadecamethylene dicarboxylate, polyethylene succinate, poly-whydroxydecanoate, and the like. For most commercial uses it is desired that the fiberforming polyester have a high melting point, and outstanding are those prepared from aromatic dicarboxylic acids wherein the carboxylic acid groups are directly attached to an aromatic nucleus, and are. symmetrically arranged thereon. Reference is made to Fibers From Synthetic Polymers, edited by Rowland Hill, Elsevier Publishing Company (1953), particularly pages 144-158 and 43645 3, for an extensive discussion of fiber-forming polyesters, to sizing of which the present invention is directed.

While this invention has been described with particular reference to preferred embodiments, it will be appreciated that variations from the exact details given herein can be effected without departing from the invention in its broader aspects.

We claim:

1. Polyester yarn sized with a water-soluble free acid form of an interpolymer of ethylene with at least one member of the group consisting of maleic anhydride and acid esters of maleic acid, said interpolymer in said free acid form having from zero to percent of its maleic units monoesterified with an aliphatic alcohol, said interpoly-mer in said free acid form having a specific viscosity of at least about 0.1 as determined on a one weight percent solution thereof in dimethylformamide at 25 C.

2. Sized polyester yarn according to claim 1, wherein said polyester is polyethylene terephthalate.

3. Polyester yarn sized with an ethylene/maleic anhydride interpolymer converted to water-soluble free acid form, said interpolymer in said free acid form having from zero to 100 percent of its maleic units mono-esterified with an aliphatic alcohol, said interpolymer in said free acid form having a specific viscosity of at least about 0.1 as determined on a one weight percent solution thereof in dimethylformamide at 25 C.

4. Polyester yarn sized with an ethylene/maleic anhydride interpolymer converted to water-soluble free acid form, said interpolymer in said free acid form having from zero to 100 percent of its maleic units mono-esterifled with a lower alkanol, said interpolymer in said free acid form having a specific viscosity Within the range of about 2 to 4 as determined on a one weight percent solution thereof in dimethylformamide at 25 C.

5. Sized polyester yarn according to claim 4, wherein said polyester is polyethylene terephthalate.

6. Polyester yarn sized with an ethylene/maleic anhydride interpolymer converted to water-soluble free acid form, said interpolymer in said free acid form having from zero to 100 percent of its maleic units mono-esterified with an aliphatic alcohol, said interpolymer in said free acid form having a specific viscosity of at least about 1 as determined on a one weight percent solution thereof in dimethylformamide at 25 C.

7. Polyester yarn sized with an ethylene/maleic anhydride interpolymer which has been esterified with a lower alkanol in an amount not exceeding 0.5 mole of said alkanol per mole of maleic anhydride in said interpolymer and converted to Water-soluble free acid form, said interpolymer in said free acid form having a specific viscosity of at least about 0.1 as determined on a one weight percent solution thereof in dimethylformamide at 25 C.

8. Polyester yarn sized with an ethylene/maleic anhydride interpolymer converted to water-soluble free acid form and essentially consisting of regularly recurring units of the formula -OH,-CH OH-CH H OH and having a specific viscosity of at least about 0.1 as determrned on a one weight percent solution thereof in dimethylformamide at 25 C.

9. Sized polyester yarn according to claim 8 wherein said specific viscosity is at least about 2.

l0. Sized polyester yarn according to claim 8, wherein said polyester is polyethylene terephthalate.

11. A method of sizing polyester yarn which comprises contacting same with an aqueous solution of a maleic anhydride and acid esters of maleic acid, said interpolymer in said free acid form having from zero to 100 percent of its maleic units mono-esterified with an aliphatic alcohol, said interpolymer in said free acid form having a specific viscosity of at least 0.1 as determined on a one weight percent solution thereof in dimethylformamide at 25 C., said aqueous solution being supplied in a concentration and in an amount sufficient to deposit a sizing quantity of said interpolymer on said yarn, and then drying said yarn.

12. Method according to claim 11, wherein said polyester is polyethylene terephthalate.

13. A method of sizing polyester yarn which comprises contacting same with an aqueous solution of an ethylene/ maleic anhydride interpolymer converted to water-soluble free acid form, said interpolymer in said free acid form having from zero to 100 percent of its maleic units monoesterified with an aliphatic alcohol, said interpolymer in said free acid form having a specific viscosity of at least about 0.1 as determined on a one weight percent solution thereof in dimethylformarnide at 25 C., said aqueous solution being supplied in a concentration and in an amount sufiicient to deposit a sizing quantity of said interpolymer on said yarn, and then drying said yarn.

14. A method of sizing polyester warp yarns to prepare them for weaving which comprises treating said yarns with an aqueous solution comprising about 2 to 15 percent by weight of a water-soluble free acid form of an interpolymer of ethylene with at least one member of the group consisting of maleic anhydride and acid esters of maleic acid, said interpolymer in said free acid 'forrn having from zero to 100 percent of its maleic units mono-esterified with an aliphatic alcohol, said interpolymer in said free acid form having a specific viscosity of at least about 0.1 as determined on a one weight percent solution thereof in dimethylforrnamide at 25 C., said aqueous solution being supplied in an amount sufiicient to deposit fromabout 0.5 to 5 percent by weight, based on the dry yarns, of said interpolymer, and then "drying said yarns.

having a specific viscosity of at least about 0.1 as determined on a one weight percent solution thereof in dimethylformarnide at 25 C., said aqueous solution be ingsupplied in an amount suflicient to deposit from about 0.5 to 5 percent by weight, based on the dry yarns, of said interpolymer, and then drying said yarns.

' 16. A method of sizing polyester warp yarns to prepare them for weaving which comprises treating said yarns with an aqueous solution comprising about 2 to 15 percent by weight of an ethylene/maleic anhydride interpolymer converted to water-soluble free acid form, said interpolymer in said free acid form having from zero to percent of its maleic units mono-esterified with an aliphatic alcohol, said interpolymer in said free acid form having a specific viscosity within the range of about 2 to 4 as determined on a one weight percent solution thereof in dimethylforrnamide at 25 C., said aqueous solution being supplied in an amount sufficient to deposit from about 0.5 to 5 percent by weight, based on the dry yams, of said interpolymer, and then drying said yarns.

17. A method of sizing polyester yarns to prepare them for weaving which comprises treating said yarns 'with an aqueous solution comprising about 2 to 15 percent by weight of an ethylene/maleic anhydride interpolymer converted to water-soluble free acid form and essentially consisting of regularly recurring units of the formula and having a specific viscosity of at least about 2 as determined on a one weight percent solution thereof in References Cited in the file of this patent UNITED STATES PATENTS 278,902 Spanagel Apr. 27, 1942 2,378,629 Hanford June 19, 1945 2,609,350 Spatt Sept. 2, 1952 2,686,137 Rossin et a1. Aug. 10, 1954 2,729,577 Bacon et al Jan. 3, 1956 2,734,001

Mecklenburgh et al Feb. 7, 1956 

1. POLYESTER YARN SIZED WITH A WARE-SOLUBLE FREE ACID FORM OF AN INTERPOLYMER OF ETHYLENE WITH AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF MALEIC ANHYDRIDE AND ACID ESTERS OF MALEIC ACID, SAID INTERPOLYMER IN SAID FREE ACID FORM HAVING FROM ZERO TO 100 PERCENT OF ITS MALEIC UNITS MONO-ESTERIFIED WITH AN ALIPHATIC ALCOHOL, SAID INTERPOLYMER IN SAID FREE ACID FORM HAVING A SPECIFIC VISCOSITY OF AT LEAST ABOUT 0.1 AS DETERMINED ON A ONE WEIGHT PERCENT SOLUTION THEREOF IN DIMETHYLFORMAMIDE AT 25* C. 